Friends of 29-year-old Krystle M. Campbell mourned her Tuesday as the second victim of the Boston Marathon bombings. On Facebook, employees of the Summer Shack restaurant in Hingham, Mass., where she was general manager said they were devastated “by the loss of our beloved Krystle.”

“She was an incredible woman, always full of energy and hard at work, but never too tired to share her love and a smile with everyone. She was an inspiration to all of us,” Summer Shack employees wrote.

Campbell’s father, William, who could not be reached for comment, told Yahoo News that he was in shock. She had been at the finish line with a friend cheering on her boyfriend, who was competing in the race.

Investigators gathering forensic evidence about the explosion that tore through the finish-line area of the Boston Marathon are looking at the type of improvised explosive devices that were used in the terror attack, seeking clues that officials hope will lead them to suspects.

The device is considered to be crude, leading some federal investigators to hypothesize that they were domestic rather than international in origin, according to three federal law enforcement officials. But while unsophisticated, the devices did show signs of having been constructed by someone with at least some experience in explosives, officials said.

Two bombs exploded on Monday, killing at least three people and injuring 176 others in what officials on Tuesday termed a terror attack. But it is unknown if the perpetrators were foreign or domestically-inspired and the type of device could be an important clue.

“It’s somebody with some basic rudimentary skills in circuitry,” said one official. “So there’s a level of experience here. And that shows some skills.”

Federal law enforcement officials said that initial signs suggest the devices were explosives that fit into backpacks, and that the assailant or assailants triggered the explosions by using timing mechanisms or set them off remotely using a cellphone.

Doctors remove pellets, nails from bombing victims | 10:03 a.m.

Authorities pressed their investigation into who was responsible for the terror bombing at the finish line of the Boston Marathon as doctors on Tuesday supplied new evidence that the wounded had been maimed by material including metal pellets.

Dr. Ron Walls, chairman of emergency medicine at the Brigham and Women’s Hospital, said Tuesday that three of the patients treated at the hospital had shrapnel that appeared to include objects he described as small, round metallic pellets about two to three millimeters in diameter, similar to BBs. He said doctors also removed about a dozen small carpenter nails from one of the patients.

Boston officials said three people died and 176 were injured in the two explosions at the end of Monday’s marathon. President Obama on Tuesday said the explosions were being investigated as an act of terrorism.

Officials have said 17 of the wounded were listed in critical condition.

Brigham and Women’s treated 31 patients, of whom 16 have been discharged. Walls said nine have been operated on and five remain in critical condition. One patient had a below-the-knee amputation and two others are still at risk of losing limbs, he said.

Dr. Mike Zinner, the head of surgery, said one patient suffered “very significant” head injuries. Zinner also said there was a patient with a penetrating neck injury, although the patient was operated on successfully. He said the trauma surgeons would likely not remove all the shrapnel from patients.

Obama labels marathon bombings a terrorist act | 8:56 a.m.

President Obama said the bombing at the Boston Marathon was being investigated as an act of terrorism and insisted that the country will not bow to such violence.

Speaking about the tragedy for the second time in as many days, Obama said the nation’s prayers go out to Boston. The two explosions on Monday killed three, including an 8-year-old boy, and wounded an estimated 176 people, Boston officials said earlier.

“This was a heinous and cowardly act and given what we now know about what took place, the FBI is investigating it as an act of terrorism,” Obama said in televised comments from the White House. “Any time bombs are used to target innocent civilians, it is an act of terror.”

“What we don’t yet know, however, is who carried out this attack or why,” the president said, pledging to use all resources to find those responsible. ”We will find whoever harmed our citizens and we will bring them to justice,” he insisted.

“We also know this,” Obama said. “The American people refuse to be terrorized.”